A legal-high advocacy group says it empathises with Southland parents concerned about their children using synthetic cannabis.

But Star Trust - which represents the majority of New Zealand's legal-high companies - says those parents should back regulation and education instead of demanding a complete ban.

Star Trust general manager Grant Hall said a complete ban would drive the synthetic cannabis market underground, out of the hands of legal retailers and into the hands of organised crime networks.

And organised crime gangs did not ask for identification, do quality control or pay taxes, he told The Southland Times yesterday.

Mr Hall's comments come after six Invercargill shops known to sell K2 and other herbal smoking products were the target of a controlled purchase operation run last Friday by Public Health South and Invercargill police.

Public Health South enforcement officer Lynn Grace said no sales of the K2 or other herbal smoking product were made after all six shops asked the volunteer youth for identification.

The result was encouraging after a previous police sting saw three of the six premises sell to a minor, Ms Grace said.

Education and compliance checks by Public Health South staff and police would continue, she said.

Last week, Lightyears Ahead Ltd - the company behind K2 - made a commitment to take the controversial legal-high brand off the market.

Mr Hall said the decision by Lightyears Ahead Ltd was welcomed but it could be some time before K2 branded products were gone.

K2 had proved popular and retailers may have stocked up on the new formula that hit the markets after a Government ban on a previous version, he said.

However, Mr Hall said a complete ban, or prohibition, on all legal highs would not work.

The way to look after communities in Southland was to regulate, educate and tax, he said.

"I understand there is a lot of frustration out there from parents and I have a huge amount of empathy with these parents who are suffering," he said.

Synthetic cannabis products were not intended for people under the age of 18 and the Star Trust supported making it tougher for young people to get their hands on the products including banning the sale of legal highs in dairies, Mr Hall said.

Doing this would be difficult until the Psychoactive Substances Bill came into force on August 1.

Synthetic cannabis was not going to go away and issues surrounding its use had to be dealt with in the open, he said.

Without regulation, there would be a black market and even now, if anyone in Southland wanted to buy synthetic cannabis without going to a retailer, they could buy it online, Mr Hall said.

"On the internet you can buy kilos of this stuff. It is absolutely ridiculous," he said. "Without sanctioned regulations, people who want to use legal highs will tap into that marketplace, which is even harder to regulate."